1. Field of the Invention
The present invention relates to a solder powder having a fine particle diameter and a method of producing the solder powder.
2. Description of the Related Art
Electronic devices such as mobile communication devices and the like are increasingly downsized and electronic components and electronic circuits installed therein are increasingly downsized, and this tendency is considered to continue in the future. The sizes of the components and circuits using a solder paste containing a solder powder are reduced, and therefore a solder paste conforming to the requirements of the fine pitch soldering technique corresponding to the line width or diameter of about 100 μm for a through hole of a substrate and wiring of an IC chip is required. In this case, the average particle diameter of the solder powder combined in the solder paste to be used is sometimes desired to be 5 μm or less. To cope with a possible future request to further downsize the electronic components and circuits, it is conceivable that a solder powder having an average particle diameter of less than 3 μm and further an average particle diameter of less than 1 μm will be increasingly requested as the solder powder to be combined in the solder paste.
Conventionally, most of solder powders have been produced by the disk atomization method and the gas atomization method, but it has been difficult to obtain a solder powder having an average particle diameter of 10 μm or less by these methods. Patent Document 1 discloses that a solder powder having an average particle diameter of 5 μm or less can be obtained even by the gas atomization method by adjusting the production conditions. However, there is no report that a solder powder having an average particle diameter of 4 μm or less was obtained by the disk atomization method or the gas atomization method.
Further, as the production method of the solder powder other than the disk atomization method and the gas atomization method, Patent Document 2 discloses a method of obtaining a solder powder by stirring oil and a solder melt. Patent Document 3 discloses a method of producing a reflow solder in the form of very fine particles. In any of the documents, a solder powder having an average particle diameter of 3 μm or less has not been obtained.
[Patent Document 1] Japanese Laid-open Patent Publication No. 2004-098118
[Patent Document 2] Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2002-519509
[Patent Document 3] Federal Republic of Germany Laid-open Patent Publication No. 4402042